Problems with setting application icon

问题:

(I'm using Visual Studio 2008, though I remember having similar problems with older versions as well.)

I've tried several different methods (many of them mentioned in this other question), but I am still having some strange issues:

1. When including an icon as a resource, it does show up as the executable file's icon immediately, but for the icon to show up on the taskbar, I have to restart the computer. Until then, it continues to show up as whatever the previous icon was. Cleaning the solution, restarting VS, doesn't have any effect. Not a really big issue, as it won't affect a released exe, but it would be nice to know where it's keeping the old icon cached and how to get rid of it.

2. No matter what I do, the icon displayed when alt-tabbing is the default app icon (square and white and generic). This includes embedding the icon in the executable, as well as setting ICON_BIG with WM_SETICON.

As for the second matter, my code looks something like:

   hIcon = (HICON)(
      LoadImage( NULL, szFilename, IMAGE_ICON, 32, 32, LR_LOADFROMFILE ) );
   if( hIcon )
      SendMessage( hWnd, WM_SETICON, ICON_BIG, (LPARAM)hIcon );

However, after sending WM_SETICON, GetLastError() returns 6, "The handle is invalid.". hWnd is a valid window handle, and hIcon appears to be a valid icon handle. I've tried searching for reasons why WM_SETICON could cause that error, and at the very least, to figure out WHICH handle it thinks is invalid, but no luck yet. I've cleared the error code immediately before calling SendMessage(), so it has to be set somewhere in the processing of the message.

I tried an alternate method, loading the icon from the exe itself, where the ID of the resource is 101 (it's the first and only resource included):

   hIcon = (HICON)(
      LoadImage( GetModuleHandle( NULL ), MAKEINTRESOURCE( 101 ),
      IMAGE_ICON, 48, 48, 0 ) );
   if( hIcon )
      SendMessage( hWnd, WM_SETICON, ICON_BIG, (LPARAM)hIcon );

... but the same thing happens; after calling SendMessage(), GetLastError() gives the same error status.

I've tried different dimensions (such as 48x48, all of which are present in the icon file), but to no different effect. I know it's definitely finding and loading the images, because if I specify a size that doesn't exist or an invalid resource ID or the wrong filename (depending on how I am loading it), it fails out long before SendMessage().

Strangely, if I specify ICON_SMALL instead of ICON_BIG, the call succeeds with no error status, but from the docs, I need to use ICON_BIG to set the icon used while alt-tabbing. Also, if I use ICON_BIG but load the 16x16 icon, I get no error status, but nothing changes.

Any ideas about what could be causing WM_SETICON to fail? Anything terribly wrong with any of the code I've posted (aside from formatting/style/casting issues, as it's simplified to just the basics)?

回答1:

I've revisited this to see if I can close out my question. I have been unable to get the app's icon to show up in the alt-tab list just through embedding it in the executable; it will show up in the taskbar, as the file's icon in Explorer, and elsewhere just fine.

I figured I'd try something simpler for setting the icon manually, and went with LoadIcon() instead, as the code below shows:

HICON hIcon = LoadIcon( GetModuleHandle(NULL), MAKEINTRESOURCE(IDI_ICON1) );
if( hIcon )
{
   SendMessage( GetHandle(), WM_SETICON, ICON_BIG, (LPARAM)hIcon );
   DestroyIcon( hIcon );
}
// ... Same for ICON_SMALL

This seems to have done the trick. I really don't know why, but so far it's the only change that had any effect. It's really not an issue I should spend any more time on, so I'll just go with this.

回答2:

I've used a single .ico file with multiple resolutions 16x16, 32x32, 48x48, 96x96 without problems, as application icon. Then windows will pick up the right size.

The windows shell have an icon cache, there is a trick to restart it without rebooting or logout from the current session, or killing explorer.exe from task manager.

回答3:

OK, this worked a treat for me :

HICON hIconSmall =(HICON)LoadImage(handleToYourApplicationInstance, MAKEINTRESOURCE(IDI_ICON1), IMAGE_ICON,16, 16, 0);

HICON hIconLarge =(HICON)LoadImage(handleToYourApplicationInstance, MAKEINTRESOURCE(IDI_ICON1), IMAGE_ICON,256, 256, 0); // Big for task bar, small loaded otherwise.

SendMessage(yourWindowHandle, WM_SETICON, ICON_SMALL, (LPARAM)hIconSmall) ;

SendMessage(yourWindowHandle, WM_SETICON, ICON_BIG, (LPARAM)hIconLarge) ;

回答4:

If found the solution for me. I created an invisible CFrameWnd application window and then a few other main windows (which are dialog windows). The magic undocumented rule is: You have to change the big icon in the first created CFrameWnd. While each window keeps it's own ICON_BIG instance, it does not use them. So it seems not possible to show different taskbar icons for different windows inside one application.

回答5:

For anyone coming to this same difficulty if you are going to change ICON_BIG you must first send WM_SETICON with ICON_SMALL and then proceed to ICON_BIG.

For example:

SetLastError(0);
SendMessage(windowHandle, WM_SETICON, ICON_SMALL, (LPARAM)iconsmallHandle);
[do error handling]
SetLastError(0);
SendMessage(windowHandle, WM_SETICON, ICON_BIG, (LPARAM)iconbigHandle);
[do error handling]

You will need to use SetLastError after the first SendMessage to clear any returned error.

If you are just setting ICON_SMALL you can ignore ICON_BIG. For whatever reason in all of my tests you must set ICON_SMALL regardless if that icon needs to change or not, before attempting to change ICON_BIG, otherwise you will always get error code 0x6 (invalid handle).